TKR: Effects of Component Rotation

- Discussion:
- if there is free movement at hip, subtalar & mid-tarsal joints rotation at the knee is not essential for restricted function of prosthetic joint;
- in contrast, an arthrodesed ipsilateral hip is a relative contra indication to knee replacement, for it prevents rotation of thigh as well as changing
position of center of gravity of body;

- Prosthetic Design:
- rotation of the femoral component:
- rotation of tibial component:
- need for component rotation:
- in constrained components which eliminate rotation, aseptic loosening of components is the most common complication;
- increased loosening forces created at limit of extension & lateral bending w/ constrained prosthesis result in higher rates of mechanical
loosening of components;
- rotation can be designed into the knee prosthesis by using a smaller radius of curvature for femoral component;
- this will reduce the area of contact with the more open tibial surface, but will also increase joint pressure and wear;
- in the report by Barrack et al, the authors sought to correlate anterior knee pain with TKR component malrotation;
- significant anterior knee pain rating at least 3 of 10 on the visual analog scale was present in 16 knees (13 patients);
- 11 patients with 14 symptomatic knees agreed to undergo CT scanning to accurately determine the rotation of the tibial and femoral components;
- epicondylar axis and tibial tubercle were used as references using a previously validated technique;
- there was a highly significant difference in tibial component rotation between the two groups w/ the patients w/ anterior knee pain averaging 6.2°
internal rotation compared with 0.4° external rotation in the control group;
- there also was a significant difference in combined component rotation with the patients w/ anterior knee pain avg 4.7° internal rotation compared
with 2.6° external rotation in the control group;
- there was no significant difference in the degree of radiographic patellar tilt or patellar subluxation between the two groups;
- patients with combined component internal rotation were more than five times as likely to experience anterior knee pain after TKA compared
with those with combined component external rotation
- ref: Component Rotation and Anterior Knee Pain After Total Knee Arthroplasty